Microalgae typically grow in water when exposed to proper nutrients, light, and carbon dioxide. Microalgae growth has been an increasing focus recently as a useful way to create biomass which can then be employed to make biofuels. Microalgae may be preferable to terrestrial crops because microalgae often grow more quickly and do not interfere with food sources. Also, microalgae can often be grown using non-potable saline water and/or waste water. Advantageously, microalgae growth is also beneficial in fixing carbon dioxide which is a greenhouse gas.
Unfortunately, advances need to be made before bioethanol can efficiently and cost-effectively be produced from microalgae. For example, the yield of glucose from the microalgae needs to be increased. This, in turn, increases any alcohol yield from the fermentation of the glucose. Similarly, any increased glucose yield from the microalgae needs to be stable and/or predictable for a given type and/or amount of nutrient(s). Moreover, compositions of nutrients for achieving effective and efficient microalgae growth are needed.
Advantageously, the present invention addresses one or more of the aforementioned needs. In one embodiment the present invention pertains to a composition comprising microalgae and a suitable growth medium. The suitable growth medium typically comprises water, a nutritionally acceptable nitrate salt, and a carbonate salt. The concentration of nutritionally acceptable nitrate salt is usually from about 75 to about 200 μM and the concentration of carbonate salt is usually from about 1 to about 6 mM.
In another embodiment, the present invention pertains to a process for making a biofuel intermediumte. The process comprises supplying light to a suitable growth medium comprising microalgae and growing the microalgae in the suitable growth medium. The suitable growth medium often comprises water, a nutritionally acceptable nitrate salt, and a carbonate salt. The concentration of nutritionally acceptable nitrate salt is typically from about 75 to about 200 μM and the concentration of carbonate salt is typically from about 1 to about 6 μM. Next, the process comprises harvesting the microalgae. Advantageously, the harvested microalgae often comprise one or more of the following characteristics: (a) the microalgae yield at least about 5% w/w more glucose than microalgae grown in a comparable composition lacking the carbonate salt; (b) the microalgae stably yield at least about 15% w/w glucose; and (c) the microalgae yield at least about 5% w/w more glucose than microalgae grown in a comparable composition with 1500 μM of the same nitrate salt.
In yet another embodiment the invention pertains to a growth medium package for microalgae. The package usually comprises a nutritionally acceptable nitrate salt and a carbonate salt. The ratio of nitrate to carbonate is typically such that when the medium package is diluted to a suitable growth medium the concentration of nutritionally acceptable nitrate salt is from about 120 to about 170 μM and the concentration of carbonate salt is from about 2 to about 5 mM.